Mike,

In terms of the number of branch circuits needed, a single 20A branch would provide up to 2400 watts, which should be ample for your list of equipment. (Unless that power amp is big enough to blow out the basement walls [Linked Image]).

I've seen some studio designs recommend balanced power, but frankly I think that in a basic set-up such as this it's overkill.

Unless your power grid is particularly noisy, I think you'll find that having a dedicated branch circuit back to the main panel would be sufficient. It might be worth opting for larger cables than code would require, as this would help keep the supply impedance down thereby reducing noise fed back into other equipment from items such as class B power amps.

If you're particularly concerned about keeping induced hum to a minimum, then maybe go with a metallic conduit installation so that the conduit will act as an electrostatic shield.